Illinois sales tax due dates for 2026
Every date below comes from the state's published deadline rule (dataset 2026.07.0) and is already moved to the next business day when it lands on a weekend or federal holiday. Your account's assigned filing frequency decides which table applies.
Monthly Illinois sales tax due dates
Rule: 20th of the month following the period.
| Period | Period ends | Return due |
|---|---|---|
| January 2026 | Jan 31, 2026 | Feb 20, 2026 |
| February 2026 | Feb 28, 2026 | Mar 20, 2026 |
| March 2026 | Mar 31, 2026 | Apr 20, 2026 |
| April 2026 | Apr 30, 2026 | May 20, 2026 |
| May 2026 | May 31, 2026 | Jun 22, 2026 (moved: 2026-06-20 falls on a Saturday) |
| June 2026 | Jun 30, 2026 | Jul 20, 2026 |
| July 2026 | Jul 31, 2026 | Aug 20, 2026 |
| August 2026 | Aug 31, 2026 | Sep 21, 2026 (moved: 2026-09-20 falls on a Sunday) |
| September 2026 | Sep 30, 2026 | Oct 20, 2026 |
| October 2026 | Oct 31, 2026 | Nov 20, 2026 |
| November 2026 | Nov 30, 2026 | Dec 21, 2026 (moved: 2026-12-20 falls on a Sunday) |
| December 2026 | Dec 31, 2026 | Jan 20, 2027 |
Quarterly Illinois sales tax due dates
Rule: 20th of the month following the period (calendar quarters).
| Period | Period ends | Return due |
|---|---|---|
| Q1 2026 | Mar 31, 2026 | Apr 20, 2026 |
| Q2 2026 | Jun 30, 2026 | Jul 20, 2026 |
| Q3 2026 | Sep 30, 2026 | Oct 20, 2026 |
| Q4 2026 | Dec 31, 2026 | Jan 20, 2027 |
Annual Illinois sales tax due dates
Rule: January 20 following the calendar year.
| Period | Period ends | Return due |
|---|---|---|
| Calendar year 2026 | Dec 31, 2026 | Jan 20, 2027 |
Illinois filing notes
- Filers averaging $20,000+/month owe quarter-monthly payments on the 7th/15th/22nd/last day of the liability month (info only).
Return and form
The principal repository-tracked return is ST-1. Paper eligibility is taxpayer-specific; electronic filing or a waiver may control.
Tracked form version: R-01/26 (form/instructions for reporting periods beginning January 2026 and after)
Paper filing posture: taxpayer specific
Official Illinois filing resources
File Illinois sales tax from reviewed data, not spreadsheets
Prophit.ai tracks every Illinois due date above inside the return workspace, builds the period from your transaction data, and produces worksheet for portal entry that a reviewer approves before anything is submitted.
Need every state at once? Download the 2026 sales tax filing calendar (CSV + ICS, all states, weekend/holiday-adjusted).
Workflow support does not by itself establish registration, filing authority, credentials, agency acceptance, or tax advice. Confirm your assigned filing frequency with the state.
Illinois sales tax filing questions
01When is Illinois sales tax due?
Monthly Illinois sales tax returns are due the 20th of the month following the period. Quarterly returns are due the 20th of the month following the period (calendar quarters). When a due date lands on a weekend or federal holiday it moves to the next business day; the 2026 calendar on this page already applies that adjustment.
02How often do you file sales tax in Illinois?
Illinois assigns a filing frequency to each account. The published cadences are monthly, quarterly and annual filing; the state assigns the frequency based on tax volume and notifies the account, so confirm the assigned basis before relying on a calendar.
03What form is used to file Illinois sales tax?
The Illinois return tracked here is ST-1. The principal repository-tracked return is ST-1. Paper eligibility is taxpayer-specific; electronic filing or a waiver may control.
04What happens if a Illinois due date falls on a weekend or holiday?
The due date moves to the next business day. In 2026, 3 of the Illinois due dates listed on this page are adjusted for a weekend or federal holiday; each adjusted date is marked in the calendar.
05Can Illinois sales tax be filed on paper?
Paper filing posture tracked for Illinois: taxpayer specific. The principal repository-tracked return is ST-1. Paper eligibility is taxpayer-specific; electronic filing or a waiver may control.
Reviewed and current as of August 22, 2026. Read the full Illinois sales tax guide for rates, sourcing, products, exemptions, and marketplace rules.